This invention relates to improved means for driving wheeled vehicles, especially electric powered vehicles. More particularly, it relates to drive means which transmit rotation to a vehicle wheel by frictional engagement of the wheel with the drive means.
The propelling of lightweight vehicles, such as tricycles, bicycles, or small four-wheel vehicles, using motor power is well known. Also, it is well known to convert pedal powered or other rider propelled vehicles for motor assisted power to reduce the effort required to pedal the vehicle. In some instances, conventional pedal powered bicycles or tricycles are converted solely to motor power by disengaging the pedal drive mechanisms. However, it is often desirable to provide conventional pedal powered vehicles with optional motor power to permit the user to choose between propelling the vehicle solely by pedaling, solely by the motor, or by a combination of the two.
Optional pedal or motor powered vehicles are especially useful for elderly users, or others who are not physically conditioned to pedal all the time, or to pedal uphill, or the like. They are also desirable where there are restrictions on the use of motors, such as on sidewalks. Also, in some locales, such as quiet zones, mobile home parks, and the like, there may be noise restrictions which prohibit the use of any vehicle, except pedal powered ones or those having quiet power sources, such as electric motors.
Thus, there has been a substantial need for vehicles adapted for motor drives, especially electric motor drives, with or without auxiliary pedal drives. Also, there has been a need for means to convert conventional pedal driven vehicles to such power driven vehicles by installing motor drives thereon.
Numerous devices have been used to mount motors, including electric motors, on bicycles, tricycles, and the like, and to transmit the power from the motors to the vehicle wheels. Some use complex gearing and clutching mechanisms. Others eliminate such gears and clutches, and these propel the vehicle by frictionally engaging the output drive shaft from the motor with one of the tires of the vehicle. This latter technique is highly desirable in achieving simplicity and economy of production.
In friction engagement devices the output shaft of the motor is provided with friction means, such as a knurled cylinder, which is pressed against the surface of a tire of the wheeled vehicle with sufficient force to substantially prevent slippage between the two. Thus, when the motor turns the knurled cylinder, a corresponding rotation is imparted to the vehicle wheel.
Various techniques have been used for pressing the drive cylinder of the motor against the vehicle wheel. Typically, the drive cylinder is pressed against the tire when the motor is stopped, and then it is locked in such depressed position by some fastening means, such as a thumb screw or nut and bolt, or the like.
Other devices employ a hand lever which the rider maneuvers against a spring bias member to force the drive cylinder against the tire and hold it there during operation of the vehicle. Still other devices employ a shift lever and toggle mechanism by which the user shifts the drive cylinder against the tire to propel the vehicle and shifts it in an opposite direction to disengage for stopping.
Some devices, such as shown in U.S. Pat. No. 4,081,048, mount motors on long lever arms longer than the radius of the vehicle wheel to permit the drive cylinder to engage the tire, aided in some instances by a spring to increase the frictional engagement force.
The prior art devices for engaging the motor with the vehicle wheel suffer various deficiencies. Those which lock the drive cylinder against the tire produce much unnecessary tire wear since such engagement is often unnecessary, for example, when the vehicle is moving downhill. Also, when the motor is not being used, as when the rider is pedalling the vehicle, the motor's engagement with the tire causes a substantial drag which is tiring and essentially prevents coasting.
The devices which use a spring biased hand lever to hold the drive cylinder against the tire can be very tiring, since they must be gripped tightly at all times that the vehicle is being motor propelled. On the other hand, those vehicles which use a shift lever and toggle mechanism may require the user to shift at each start and stop of the vehicle. This may pose safety hazards when an emergency stop requires quick disengagement of the motor from the wheel.
These and other deficiencies of the prior art may be elimated or greatly alleviated in accordance with the present invention.